1. Field of the Invention
The present invention relates to an organic electroluminescence device which is able to prevent the device from being damaged due to an outer shock and a fabrication method.
2. Description of the Related Art
Large flat panel displays having various functions that are essential in the image industry field of the 21st century information society. Flat panel displays include displays using an organic material and display using an inorganic material. The flat panel displays using the organic material comprises liquid crystal display (LCD), which is in wide use, and electroluminescence display (ELD), plasma display panel (PDP) and field emission display (FED).
The organic ELD is a flat panel display device using an electroluminescence phenomenon, that is, light is generated when an electric field greater than a certain degree is applied across an electroluminescence material. The organic ELD has the advantages of rapid response time, when compared to an LCD device, and high brightness. Research in organic ELD is proceeding in the basic light emitting device and is actively being applied in developing pixels for a large flat panel display.
FIG. 1 is a view showing a related organic ELD. As shown in FIG. 1, the organic ELD includes: a transparent substrate 125; an anode electrode 105 of transparent material, such as indium-tin-oxide (ITO), formed on a transparent substrate 120; an organic light emitting layer 110 formed on the anode electrode 105, a cathode electrode 115 having a low work function disposed on the an organic light emitting layer 110. The transparent substrate 120, the electrode layers 105 and 115 and the organic light emitting layer 110 are all referred to as a lower substrate 125.
The organic light emitting layer 110 comprises a plurality of layers for emitting the light smoothly, generally includes: a hole injection layer 110a, a hole transporting layer 110b, a light emitting layer 110c, an electron transporting layer 110d and an electron injecting layer 110e. And when current is applied, the holes from the anode electrode 105 and electrons from the cathode electrode 115 are injected into the organic layer to form exciton on the light emitting layer 110c, and as the exciton is extinguished, the light corresponding to the difference between energies of the lowest unoccupied molecular orbital (LOMO) and the highest occupied molecular orbital (HOMO).
FIGS. 2A and 2B are side cross sectional view and plane view showing an organic ELD. As shown in FIG. 2A, an upper substrate 205 for encapsulating the lower substrate 125 is formed on upper part of the lower substrate 125. Generally, the organic light emitting layer is easily contaminated by humidity or impurities from the outside. In the case when the organic light emitting layer is contaminated by the humidity or impurities, the organic ELD has inferior display qualities. To block the humidity from entering into the organic ELD and to protect the device from outside impurities, the upper substrate 205 is attached to the lower substrate 125 by a seal pattern 210.
FIG. 2B is a plane sectional view in line 11—11 direction shown in FIG. 2A. As shown in FIG. 2B, the upper substrate 205 and the lower substrate 215 are attached to each other by the seal pattern 210 printed on an outer portion of the upper substrate 205. On the other hand, in the case when the organic light emitting layer is in contact with oxygen or humidity, the organic light emitting layer dissolves and the luminescent property of the organic light emitting layer decreases. Therefore, a desiccant film 215, including nylon, is attached on an area of the upper substrate 205 corresponding to the organic light emitting layer to prevent oxygen or humidity from infiltrating into the organic light emitting layer 110.
The upper substrate 205 and the lower substrate 125 are constructed, as discussed above, and attached together with the seal pattern 210. The cell gap between the upper substrate 205 and the lower substrate 125 is determined and maintained by the seal pattern 210. Using the seal pattern 210 to maintain and determine the cell gap is similar to the use of a seal pattern in an LCD device. In the LCD device, if the lower substrate on which TFT is formed and the upper substrate on which color filter are compressed together there is no problem since the liquid crystal is somewhat resilient.
In the case of the organic ELD, if the pressure is applied to the lower substrate 125 or to the upper substrate 205 after attaching the upper and lower substrates 205 and 125, the electrode layers 105 and 115 or the organic light emitting layer 110 can be damaged. Because the electrode layers 105 and 115 and the organic light emitting layer 110 are formed with a vacuum deposition method, the strength and adhesion property of the layers are very weak and can be easily separated by a little pressure. The damage to the electrode layers 105 and 115 or the organic light emitting layer 110 is even worse due to the bending of the substrate. More particularly, a point defect can occur. A point defect is when a pixel unit becomes inoperable. Thus, pressure applied to an organic ELD, which bends the substrate of an organic ELD, can cause severe defects across the display panel of an organic ELD.